1. Field of the Invention
This invention relates generally to nuclear magnetic resonance (NMR) imaging (MRI) of living systems, and, more particularly to a method for remote NMR imaging of such living systems, remote detection affording potentially greater resolution of the areas being imaged, and facilitating the creation of portable MRI devices.
2. Background of the Invention
Conventional medical MRI requires a strong magnetic field provided by a superconducting magnet in order to obtain good sensitivity and spatial resolution. Such MRI equipment requires cryogenic support, and accordingly it is stationary, and must be used in a hospital-like setting. In addition, because the superconducting magnets, as well as the RF and gradient coils which are required for three dimensional imaging must be large enough to accommodate the subject to be imaged, and because of the dimensional issues involved, resolution of the imaged areas deep inside the body can be less than optimum.
One of the drawbacks of conventional NMR in medical imaging is the low filling factor. The filling factor relates to the size of the area to be interrogated by NMR compared to the area viewed by the sensor. The smaller the filling factor, the less detailed the image. In interrogating a voxel (a unit of volume, generally around 1 mm3), of a section of living tissue such as the brain, for example, both the magnet and the detector coils are spaced some distance from the subject section. As is apparent from consideration of looking at a portion of the inner brain, the volume of the voxel is quite small in relationship to the volume within the space contained by the sensor. While fairly good readings can be obtained at voxels near the outer reaches of the brain, just underneath the skull, using (for example) a surface coil, getting accurate readings of voxels deeper within the brain is problematic. Thus, if one could bring the sensor closer to the area to be interrogated, it would be possible to increase the filling factor and thus sensitivity.
In addition to sensitivity, conventional MRI (most commonly employing large superconducting magnets of high magnetic field) is not always suitable for at least the following: a) patients with metal implants; b) claustrophobic patients and infants; and c) patients under constant monitoring by electronic devices. In addition, the expense and immobility of the MRI apparatus (most importantly the magnet) make it inapplicable in many circumstances, including third world countries and for medical practices outside of hospitals. The cryogenics associated with the superconducting magnets contribute substantially to the high maintenance and initial cost of MRI instruments. Any approach to MRI that does not require high, homogeneous magnetic fields and that uses a simpler approach for detection would significantly expand the applicability of this analytical approach.